During the in situ breaking down of bitumen from oil sand by means of steam and horizontal bore holes according to the SAGD (Steam Assisted Gravity Drainage) method the problem arises with thin bitumen strata in particular that only an economically limited quantity of bitumen can be tapped. In the most favorable instance this is around 40 to 60% of the bitumen present in the reservoir but much less in the case of thin strata. The reason for this is the limited width of the growing steam chamber, which is typically around twice as wide as it is high. For a high yield in flat reservoirs (20 to 30 m) this means that an injection pipe must be provided to introduce energy every 40 to 60 m above the extraction pipe. The two pipes, one on top of the other, are known in the pertinent prior art as so-called well pairs.
A specific SAGD method for extracting very heavy oil is known from U.S. Pat. No. 6,257,334 B1, in which, in addition to a so-called well pair consisting of pipes one on top of the other, further elements are also present, which are intended to improve the heating of the region. Also in WO 03/054351 A1 a facility for the electrical heating of certain regions is described, with which a field is generated between two electrodes, heating the region in between them.
In the prior art the well pairs are provided at small intervals, incurring high costs for horizontal boring and piping. Alternatively high yields would have to be sacrificed to save costs.